The present invention relates to inertial exercise equipment, and more specifically, to apparatuses and methods for substantially uniform transition between eccentric actions and concentric contractions of muscles.
Generally, muscles undergo a number of different types of contractions during everyday activity. A concentric or isotonic contraction is a shortening of the muscle when the muscle is acting under tension. An isometric contraction occurs when the muscle is under tension but maintains a constant length. An eccentric muscle action is a lengthening of the muscle when the muscle is acting under tension.
Under typical circumstances, concentric contractions of a muscle oftentimes produce an acceleration of an object, whereas eccentric actions of the muscle provide for the deceleration of the object. In other words, concentric contractions usually provide the activation or creation of energy in an object, while eccentric actions provide the braking effect. Most often, the transition between these two different types of muscle contractions occur at the peak of inertial energy. For example, when a pitcher throws a baseball at 80 miles per hour, concentric contractions of certain shoulder muscles accelerate the baseball and arm up to that velocity. When the arm and ball reach the peak of inertial energy, the pitcher releases the ball and the concentric contractions of that shoulder muscle transition into eccentric muscle actions that act to decelerate the velocity of the arm back to rest. During eccentric muscle actions, the inertial force created by the momentum of the pitching arm works against the muscle creating the muscle tension and elongation. Swinging a tennis racket, a baseball bat, and a golf club are other sports related examples illustrating a transition from concentric contractions to eccentric actions at the peak of inertial energy.
Eccentric muscle actions or deceleration activities produce muscle injuries more often than concentric contractions or acceleration activities. Strains are most often caused by over-loading a muscle, which usually results from a forced stretching of a contracted muscle. Because muscle tensions created by eccentric actions are generally much higher than those generated by concentric contractions and because more force can be generated during eccentric exercises, strains are commonly caused by eccentric muscle actions.
It is important to exercise muscles by eccentric training because such training is a very effective way to strengthen muscles, particularly for specific functional movements. Eccentric actions produce the maximum stress on the muscle-tendon unit, and it is necessary to strengthen the muscle-tendon unit to withstand these stresses in order to cope with and prevent injury caused by such eccentric muscle actions.
Studies have shown that when an eccentric action was the cause of an injury, the most effective rehabilitation program includes similar eccentric training exercises. Also, eccentric strength training produces better strength gains than concentric training and is a more effective form of rehabilitation strength training.
The most common strengthening technique utilizing a combination of concentric and eccentric contractions is simple weight lifting. However, weight lifting also includes resistance loads, specifically those caused by gravity. Therefore, the weightlifter is constantly working to overcome the resistance loads as opposed to concentrating on acceleration and deceleration forces. This does not provide the trainer with the beneficial transition of purely acceleration forces to deceleration forces. Rather, a weightlifter""s muscles undergo concentric contractions when raising the weight to a rest position and undergoes eccentric muscle actions when the weight is being lowered to a rest position. In other words, when the weight is being lifted, the lifter does not use eccentric muscle action to decelerate the weight to the rest position. Instead, gravity is allowed to slow the velocity associated with raising the weights. In turn, when the weight is being lowered, the muscles do in fact undergo eccentric actions. However, there is no direct transition from concentric contractions, and the deceleration forces are increased substantially by the gravity force acting on the weight. More importantly, there is no inertial energy generated in the weight when the muscles transition from concentric contractions to eccentric contractions, as the weight begins from rest at this point.
A number of exercise techniques and equipment exist that employ acceleration and deceleration forces for concentric and eccentric muscle training. Although such techniques and equipment often provide for a uniform transition from concentric contracting to eccentric action of the muscles at the point of peak generated inertial energy, they each typically possess certain undesirable attributes.
For example, many inertial exercise devices and techniques utilize a mass that is connected (often by a tether) to a body part and that is slidable along a linear track. A body part accelerates the mass along the track, and thereafter the motion of the mass is converted to a motion that can be decelerated by the body part. An example of such a device is disclosed in FIG. 4 of U.S. Pat. No. 4,632,392 issued to Peyton et. al. Unfortunately, adverse resistance loads usually accompany such devices and techniques, and are caused by the friction of the mass sliding on the track. This friction load tends to increase the concentric contraction necessary to accelerate the mass, and tends to decrease the eccentric action necessary to decelerate the mass. The friction between the track and the mass is dependent upon the amount of mass used for the exercise. Therefore, the greater the mass used on the track, the larger the inequality between the acceleration and deceleration forces.
Other exercise devices and techniques employ one or more rotating or orbiting masses to harness rotational inertia forces for concentric and eccentric muscle training. Two examples of such devices and techniques are disclosed in FIGS. 1 and 5 of the Peyton Patent. In addition to the friction load problems described above, such devices and techniques can have limited adjustability. For example, where the mass moved is upon a track, adjustability is generally only possible by changing mass size (and not the mass path). As another example, the size of the exercise equipment is often fairly large, and can require balanced loading of multiple weights for proper operation (see FIG. 5 of the Peyton Patent).
In light of the above design requirements and limitations, a need exists for an inertial training apparatus which provides a substantially uniform transition between muscular concentric contraction and muscular eccentric action at the peak of generated inertial energy, provides substantially equal and proportional acceleration and deceleration forces, provides low or negligible resistance loads, provides for adjustment in magnitude and rotational radius of even a single weight to modify the acceleration and deceleration loads, and provides for ease of manufacture and minimal material costs. Each preferred embodiment of the present invention achieves one or more of these results.
The present invention is an inertial training apparatus and method preferably utilized for strength training and rehabilitation strength training of muscles. The present invention allows for the generation of inertial forces by accelerating a mass by a concentric contraction of at least one muscle and converts the inertial forces of the mass into an equivalent or substantially equivalent eccentric action of the muscle or muscle group used to decelerate the mass. The transition of acceleration forces into deceleration forces preferably occurs when the inertial energy of the mass reaches its peak. This deceleration is the reflexive stimulus resulting in increased concentric muscle contraction, which is a desired result of optimal strength training for power. Such power is generated by the utilization of stored elastic energy within the muscle being trained, and is the result of stretch reflex of the muscle (commonly referred to as the stretch-shortening cycle). Preferably, the inertia generated by the mass is rotational inertia. The mass is thereby preferably rotationally accelerated and rotationally decelerated about an axis. A tether can be coupled between the mass and a body part of a user to transfer the tension forces provided by the body part to accelerate the mass and, in turn, those provided by the body part to decelerate the mass. The inertial training apparatus also allows for cyclical repetition of the muscular loading due to the acceleration and deceleration of the mass.
In highly preferred embodiments of the present invention, the inertial training apparatus includes a frame and a swing arm. The swing arm is rotatably mounted to the frame to preferably allow for almost frictionless rotation about a substantially vertical axis. Because the movement is relatively frictionless, resistance forces interfering with the equality of the concentric and eccentric actions are negligible. Preferably, the mass is adjustably coupled to the swing arm. More preferably, the mass is capable of being positioned in variable locations along the length of the swing arm to modify the moment of inertia, effectively increasing or decreasing the forces necessary for the acceleration and deceleration of the mass. The acceleration and deceleration loads can therefore be varied by either moving the mass along the length of the swing arm or by increasing or decreasing the mass in a single position on the swing arm. Because the swing arm preferably extends only in one direction from the axis, an adjustment of a counterweight is not necessary such as would exist with a system utilizing a rotating disc. Preferably, the apparatus also includes a primary tether guide. More preferably, the primary tether guide is coupled to the frame and is positioned near the intermediate rotational position of the swing arm where acceleration forces are transferred into deceleration forces. Most preferably, the tether is positioned through the primary tether guide and has one end attached to the swing arm and another end attached to a handle. The handle can be easily and comfortably engaged by a body part of the user designated to exercise a certain identified muscle or muscle group.
In one preferred embodiment of the present invention, the inertial training apparatus includes a vertical assembly. Preferably, the vertical assembly includes a vertical member having an intermediate tether guide and an upper and lower tether guide coupled thereto. The tether preferably extends from the end of the swing arm through the primary tether guide, the intermediate tether guide, and finally through either the upper or the lower tether guide. The alternate upper and lower tether guides are provided to allow for more comfortable and effective exercise in either an elevated or lowered position.
More information and a better understanding of the present invention can be achieved by reference to the following drawings and detailed description.